Small packages for semiconductors with short leads are desirable for forming electronic circuits which are compact. However, such small packages provide problems in terms of dissipating heat from packaged power devices used in the electronic circuits. In many cases the heat dissipating capacity of the leads only is not sufficient to provide reliable operation of the power device. In the past heat sinks have been attached to such devices to help dissipate the heat.
Another factor in forming compact circuits is the amount of space required for wire bonds in conventional packages. Thus it would be desirable to provide a package for a power device which efficiently dissipates heat while minimizing the amount of area on a circuit board for the package.
The arrangement of two power devices which have a common high current input or output terminal are found in such circuits as synchronous buck converters. Synchronous buck converters are commonly used as power supplies for cell phones, portable computers, digital cameras, routers, and other portable electronic devices. Synchronous buck converters shift DC voltage levels in order to provide power to programmable grid array integrated circuits, microprocessors, digital signal processing integrated circuits, and other circuits, while stabilizing battery outputs, filtering noise, and reducing ripple. These devices are also used to provide high current multiphase power in a wide range of data communications, telecommunications, point-of-load and computing applications.
FIG. 1 shows a block diagram of a typical synchronous buck converter 10. The converter has a high side FET 12 and a low side FET 14 which are driven by a pulse width modulation (PWM) IC 16. The Q1 and Q2 devices 12, 14 can be configured as discrete devices which require optimal layout to reduce parasitic resistances 18 and inductances 20 caused by the connection of the source of high side FET 12 to the drain of the low side FET 14 on a printed circuit board (PCB).
US Patent Application Publication No. 2005/0285238 A1, published Dec. 29, 2005, inventors Joshi et al., discloses an integrated transistor module including a leadframe structure that defines a low side land and a high side land. A low side transistor is mounted on the low side land with its drain electrically connected to the low side land. A high-side transistor is mounted on the high-side land with its source electrically connected to the high side land. A stepped portion of the leadframe structure electrically connects the low and high side lands and thus also the drain of the low-side transistor with the source of the high-side transistor.
Although the integrated transistor module of the latter published patent publication is useful for the applications for which it was intended, the module footprint is not a common one in the industry.
There is thus a need for an improved integrated power device module that can be used in circuits such as synchronous buck converter circuits that offer a solution to these problems.